More boundaries crumble following the latest flutter of results
In 1976 an unexpectedly beautiful creature emerged from a theoretical study of 2D crystals in a magnetic field. With its repeating recursive flutter of wings, ‘Hofstadter’s butterfly’ showed how the effects of an applied magnetic field and the electrostatic potential from a two-dimensional crystalline lattice play out, and would help explain electron behaviour in various quantum systems.
Yet for almost forty years it remained a figment of theory, until a flurry of experiments with graphene – honeycomb sheets of carbon atoms – layered on boron nitride revealed the butterfly in experimental data for the first time. Ten years later another series of experiments – two observing the Hofstadter butterfly and one further exploiting the effects that brought it into view experimentally – have highlighted the vast scope that layered 2D material systems can explore, further blurring the boundary between two and three dimensions, and even the distinction between periodic and aperiodic structures.